1. Field of the Invention
The present invention relates to a method for joining a core member and grippers in a polymer insulator including a core member, an outer sheath comprised of a body and caps, which are provided around the core member, and the grippers provided on both ends of the core member. Moreover, the present invention relates to the polymer insulator.
2. Description of the Related Art
Heretofore, a polymer insulator has been known, which include a core member, an outer sheath comprised of a body and caps, which are provided around the core member, and grippers provided on both ends of the core member. Moreover, in the polymer insulator, the joining of the core member and the grippers has been performed in such a manner that, for example, using divided dice, the respective dice being pushed toward the center of the core member with equal strengths to one another, and thus the grippers are clinched to the core member. As described above, the grippers are clinched (attached by pressure), and thus tensile strengths of joint portions of the core member and the grippers are maintained.
Conventional polymer insulators have been able to meet various properties conventionally required therefor. However, the demand to improve the tensile strengths of the joint portions of the grippers and the core member has increased in recent years. If the tensile strengths of the joint portions can be improved, then sufficient tensile strengths can be obtained even if the overall length of the grippers is shortened. It is thus made possible to shorten the clinch and grip length of the grippers, and to reduce the weight of the grippers and the cost due to the reduction of the number of clinching, and further to improve the performance of the polymer insulators. However, a technique capable of effectively improving the tensile strength between the joint portions of the grippers and the core member has not been discovered yet.